1. Field of the Invention
The present invention relates to a chemically amplified negative resist composition to be used for processing of a semiconductor or photomask blanks, etc., and a resist patterning process using the same.
2. Description of the Related Art
In recent years, as an integrated circuit progresses toward a higher integration, a finer circuit pattern profile has been required. Among these, a chemically amplified resist using an acid as a catalyst has been exclusively used in the patterning process of the size of 0.2 μm or less. Also, a high-energy beam such as ultraviolet beam, far ultraviolet beam, an electron beam, etc., has been used as an light source at this time, in particular, an electron beam lithography which has been utilized as an ultrafine processing technology is indispensable as a processing method of a photomask blank when a photomask for a semiconductor manufacturing is to be produced.
A polymer containing a large amount of aromatic skeletons having an acidic side chain, for example, a polyhydroxystyrene, has been utilized as a resist composition for KrF excimer laser, but it shows remarkable absorption in wavelength of near 200 nm of the light, so that it has been never used as a resist composition for ArF excimer laser. However, it is an important material in the point that high etching resistance can be obtained as a resist composition for an electron beam or a resist composition for extreme ultraviolet (EUV), which is a useful technology for forming a smaller pattern than the processing limit by ArF excimer laser.
As such a resist composition to be used for photolithography, there are a positive type in which an exposed area is dissolved to form a pattern and a negative type in which an exposed area is remained to form a pattern, and a type which can be used easier is selected depending on the form of the resist pattern to be required. The chemically amplified negative resist composition generally contains a polymer which is dissolved in an aqueous alkaline developer, an acid generator which is decomposed by exposure light to generate an acid and a crosslinking agent which forms crosslinking between polymers using an acid as a catalyst to insolubilize the polymer in the above-mentioned developer (in some cases, the polymer and the crosslinking agent are integrated), and a basic compound to control diffusion of the acid generated by the exposure is further added in general.
As the alkali soluble unit constituting the polymer which is dissolved in the above-mentioned aqueous alkaline developer, a type of using a phenol unit may be mentioned. In the prior art, a large number of such a type of the negative resist compositions have been developed particularly for exposure by KrF excimer laser beam. However, a phenol unit thereof does not have light transmittance when the exposure light has a wavelength of 150 to 220 nm, so that these have not been used as a composition for the ArF excimer laser beam. But in recent years, it has been attracted attention again as a negative resist composition for exposure light of a short wavelength such as an electron beam (EB) and EUV which is an exposure method for obtaining a finer pattern, and, for example, Patent Document 1, Patent Document 2 and Patent Document 3 have been reported.
By the way, in the above-mentioned photolithography, for the purpose of controlling resist sensitivity or pattern profile, various improvements by selection or combination of the materials used for the resist composition, and modification of the processing conditions, etc., have been investigated. As one of the focuses on the improvement, there is a problem of diffusion of an acid which causes important effect on resolution of the chemically amplified resist.
An acid diffusion controlling agent is a material to suppress acid diffusion, and is in fact an essential component to improve performances of the resist, in particular resolution. Various investigations have been done on the acid diffusion controlling agent, and amines or weak acid onium salts have generally been used. As an example of the weak acid onium salt, in Patent Document 4, it has been disclosed that good resist pattern can be formed without forming T-top, difference in line widths between isolated pattern and dense pattern, and standing wave by adding a triphenyl-sulfonium=acetate. In Patent Document 5, it has been stated that sensitivity, resolution and exposure margin have been improved by the addition of a sulfonic acid ammonium salt or a carboxylic acid ammonium salt. Also, in Patent Document 6, it has been stated that a resist composition for KrF and an electron beam comprising a combination containing a photoacid generator which generates a fluorine-containing carboxylic acid is excellent in resolution, and process admissibility such as exposure margin, depth of focus, etc., have been improved. Further, in Patent Document 7, it has been also stated that a resist composition for F2 laser light comprising a combination containing a photoacid generator which generates a fluorine-containing carboxylic acid is excellent in line edge roughness (LER), and a problem of footing profile has been overcome. Whereas the proposals of the above-mentioned four documents relate to the compositions used for KrF, an electron beam and F2 lithography, in Patent Document 8, a positive photosensitive composition for ArF excimer laser exposure containing a carboxylic acid onium salt has been disclosed. These are to suppress the acid decomposition reaction of the acid-labile group and make the acid diffusion distance small (to control) by exchanging a strong acid (sulfonic acid) generated from the other photoacid generator by exposure with weak acid onium salt to form a weak acid and a strong acid=onium salt so that a strong acid (sulfonic acid) having high acidity is exchanged to a weak acid (carboxylic acid), and thus, it apparently acts as an acid diffusion controlling agent.
However, when patterning is carried out by using the above-mentioned resist composition containing a carboxylic acid onium salt or a fluorocarboxylic acid onium salt, it involves the problem that LER is large, so that development of an acid diffusion controlling agent which can reduce LER has been desired.